Methods are currently known for drilling and milling glass sheets, as obtained following cutting from the original production format to the destination formats and, in most cases, following the grinding of the perimetric edge. In principle, the grinding, drilling and milling operations can be applied to any step of the working of the glass sheet after cutting, for example before its use as is to compose the insulating glazing unit or as a mandatory operation before tempering or as preparation of the glass sheet to obtain a regular surface finish and geometry or for particular uses such as the composition of the structural insulating glazing unit.
The grinding of the perimetric edge is performed for several reasons, which are listed here not in order of importance: the first one relates to safety in handling the sheets, in which the edges would be dangerously sharp if they were not ground; the second one relates to the elimination of edge defects of the sheets, typically so-called “micro-cracks”, which might trigger breakages of the sheet in the subsequent working steps (particularly tempering), as well as in subsequent states of transport or use; the third one can be simply in order to define the format of the glass sheet with better dimensions, geometry and surface finish than can have been obtained with the first work step, i.e., cutting, which leaves rough edges, and this is done for architectural uses, for use in interior decoration, and in particular for use in the composition of the structural insulating glazing unit (used as enclosure of buildings), the geometry of which is required to be precise in its dimensions and shape and the edge finish of which is required to be uniform in view of the optical effects linked to these configurations; additional reasons for resorting to grinding of the perimetric edge may be the most disparate.
In the case of architectural or interior decoration uses, the need is frequent to have glass sheets provided with holes with a generally beveled cylindrical geometry or with openings having a rectangular or contoured shape that affect or not the peripheral margin. A classic example is glass doors, where the interface with the hinges requires the presence of holes or openings and the interface with the handle or lock also requires the presence of holes or openings. Respectively, holes having a cylindrical, usually beveled, geometry are obtained by means of the drilling operation and the openings are obtained by means of the milling operation. Operations commonly already performed by means of machines known as drills for the first case, milling machines for the second case, or drills/milling machines for combined cases, but in manual or semiautomatic conditions (since the placement of the sheet and of the fixing constraints entail manual interventions) or automatic conditions (but with the problem of the vibration of the portion of the glass sheet proximate to the tool unsolved or partially solved).
The glass sheets can have different shapes depending on use: for example, they can be provided with coatings (of the reflective, low-emissivity, selective type) which provide barrier capabilities against optical radiation (both thermal and luminous); they can be composed of two or more glass sheets separated by one or more membranes of plastic material (of the type of PVB=Poly Vinyl Butyral type or of the EVA=Ethylene Vinyl Acetate type), which give intrusion prevention, vandalism prevention, bulletproofing, security characteristics; they can undergo the tempering treatment (after the grinding/drilling/milling operations), which gives the characteristic of fracture into microelements for safety purposes, such microelements not being able to injure. These three classes of shapes can be even combined with each other with various possibilities.
As regards the operations for drilling and milling glass sheets, protection at the industrial property level is particularly crowded, in view of the development of the use of glass sheets in architectural fields related to enclosures of buildings, stairs and railings, and to interior decoration, and in recent years also due to the spread of eastern manufacturers of machines dedicated to these operations.
A selection of the patent titles related to the most pertinent background art, with respect to the disclosure that will be described hereinafter, is as follows:                for the solution in which the sheet is arranged vertically and can move transversely with respect to the working bridge (or bridges) provided with the working head (or heads), the latter being movable transversely with respect to the glass sheet: CN 203187555(U), by Glassman Machinery Beijing Co. Ltd., filed May 8, 2013 and granted Sep. 11, 2013;        for the solution in which the sheet is arranged horizontally fixed and the working bridge can move longitudinally with respect to the glass sheet, provided with the working head, the latter being movable transversely with respect to the glass sheet (longitudinally is understood to be along the direction that is parallel to the long side of the glass sheet, transversely is understood to be along the direction that is parallel to the short side of the glass sheet): EP 1 270 147 A2, by Bimatech S.r.l., filed Jun. 18, 2002 with priority Jun. 19, 2001.        
None of these disclosures leads to the inventive concept of the present application, which in summary includes performing, with a substantially vertical arrangement of the glass sheet having a rectangular or other than rectangular shape, in a single machine and automatically, the drilling and milling work in any portion of the glass sheet, keeping the glass sheet fixed during work with respect to the working bridges and keeping the portion affected by work validly stabilized against vibrations by way of mechanisms that interact with the plate at right angles, longitudinally and transversely and belong to the head of the two working heads that is not used for milling, and render the glass sheet integral with respect to the working bridges.
CN 203187555 (U) moves the glass sheet with respect to the working bridges during work that has a longitudinal orientation and during this work and also in other work the coupling with respect to the glass sheet, proximate to the portion of sheet affected by the work and therefore subjected to stresses and vibrations, acts only at right angles to said sheet and not in the longitudinal direction (i.e., on the plane of the glass sheet and parallel to its long side) and transverse direction (i.e., on the plane of the glass sheet and parallel to the short side thereof).
EP1270147 A2, in addition to acting on a sheet with a horizontal arrangement, uses an array of suckers constituted by n rows, each of which can be adjusted manually and in each of which m suckers are adjustable and can be activated automatically so that from 1 to n×m suckers can interact with the lower face of the glass sheet in order to retain such sheet proximate to all the regions in which it is worked. Therefore, fixing of the sheet during work is entrusted to a large plurality of suckers (which cannot always be arranged, or are difficult to arrange, in an ideal position to contrast vibrations and shear stresses produced by the working tools) and associated mechanisms, which moreover are not all automatic, and this entails excessive costs in investment, operation and maintenance. Moreover, this machine, by working with a horizontal arrangement of the glass sheet, entails complex operations that are onerous in terms of time and risky in terms of safety, since they are manual, though being controlled by lifting means, for loading and unloading the glass sheets. Moreover, since this machine does not have a tailstock, it cannot perform all types of drillings.
The background art also provides the solution of resorting, for the operations for drilling and milling glass sheets, to one or more nozzles that perform this work by means of a jet of water at extremely high pressure mixed with abrasive particles; however, this type, besides being beyond the scope of the IPC B24B9/10 classification, has aspects of considerable cost and technological complications for performing bevels or profiles that affect the thickness of the glass sheets.